Video signals may be characterized by multiple parameters, such as bit-depth, color space, color gamut, and resolution. An important aspect of a video signal's characteristic is it dynamic range. Dynamic range (DR) is a range of intensity (e.g., luminance, luma) in an image, e.g., from darkest black to brightest white. As used herein, the term ‘dynamic range’ (DR) may relate to a capability of the human psychovisual system (HVS) to perceive a range of intensity (e.g., luminance, luma) in an image, e.g., from darkest black to brightest white. In this sense, DR relates to a ‘scene-referred’ intensity. DR may also relate to the ability of a display device to adequately or approximately render an intensity range of a particular breadth. In this sense, DR relates to a ‘display-referred’ intensity. Unless a particular sense is explicitly specified to have particular significance at any point in the description herein, it should be inferred that the term may be used in either sense, e.g. interchangeably.
As with the scalable video coding and HDTV technologies, extending image DR typically involves a bifurcate approach. For example, scene referred HDR content that is captured with a modern HDR capable camera may be used to generate a lower dynamic range (LDR) or standard dynamic range (SDR) version of the content, which may be displayed on conventional SDR displays. In one approach, generating the SDR version from the captured VDR version may involve applying content mapping operations, such as a global tone mapping operator (TMO) to intensity (e.g., luminance, luma) related pixel values in the HDR content.
Layered encoders may transmit a base layer (BL), one or more enhancement layers (EL), and metadata related to the encoding process to a downstream receiver. Such an approach typically consumes less bandwidth than would be consumed in sending both the HDR and SDR contents directly into the bitstream. Compatible decoders that receive the bitstream sent by the encoder may decode and render the SDR on conventional displays. Compatible decoders however may also use the enhancement layer and the metadata to compute a predicted version of the HDR content therefrom, for use on more capable displays. It is the purpose of this invention to provide novel methods for improved efficiency in the coding of HDR data.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.